1. Field of the Invention
This invention relates to automatic door operators having a drive screw within a guide means, and more particularly to a coupling assembly for the drive screw and the guide means.
2. Description of the Prior Art
Garage door operators have been manufactured and sold for over 40 years. The concept of a longitudinally stationary but rotating screw to act on a traveling nut to open an overhead-type garage door was shown to have been conceived over 45 years ago in U.S. Pat. No. 2,056,174. Cable-operated or chain-operated garage door operators have also been proposed, for example, as shown by U.S. Pat. Nos. 3,439,727 and 3,444,650. Typically, garage door operators provide a traverse of the door operator mechanism of about eight or nine feet in order to accommodate the usual height of the garage door plus the 90.degree. angle through which the door turns.
In the chain-type garage door operator that has been manufactured, it has been customary for many years to shorten the package in which the door operator is shipped by cutting the guide channel into two or three parts which may by spliced together. The channel which was previously nine feet long could comprise three parts of about three feet in length each. The screw drive door operators which were marketed at that time retained a one-piece screw and a one-piece guide means of about nine feet in length, which made the package costs higher and, more importantly, made the shipping and storage costs higher because the shipping charges are usually based upon the cubic volume of the package rather than upon the weight.
Screw drive garage door operators have now been developed in which the guide means is in two or three parts and the screw is in two or three parts. Initially, the screw and the guide means were interconnected by coupling means which had an interconnecting link with a pivot pin at each end pivoted to the screw parts. In one early version of such an operator, the guide means and screw parts were folded for shipment and then, upon installation, were straightened to be coaxial, and splice plates were bolted onto the sides of the guide means to maintain the coaxial alignment of the screw parts. An example of this type of coupling assembly is shown in U.S. Pat. No. 4,241,540, issued to Depperman.
Some of the problems with this construction were the weakness of the screw coupling relative to the rest of the screw, the alignment of the guide means when it was properly straightened, and the whipping of the screw during rotation which, because of two different pivot points, acted somewhat like a universal joint to whip around inside the guide means. The coupling for the two screw parts also had so many different parts that the possible cumulative error in the tolerance of all these manufactured parts made it possible that the threads on the two screw parts could be mismatched relative to the transversing partial nut, and thus the nut would fail to traverse this elongated coupling. Also, the very many parts in this coupling and the necessary clearance between the parts to premit folding caused the coupling to tend to destroy itself upon repeated reversals of the screw.
Many of these problems were overcome by the screw coupling disclosed in U.S. Pat. No. 4,352,585, issued to Spalding, Instead of being connected together at the factory by a double pivot connection, the screw parts were shipped to the customer in a disconnected condition, but one in which the coupling could be readily connected in a proper phase to avoid mismatch of the threads. A suitable coupling was also provided for the guide means, but the screw coupling and the guide means coupling were located longitudinally at approximately the same location along the length of the door operator. Since the screw coupling was the weakest part of the screw and the guide means coupling was the weakest part of the guide means, these weak portions were located together, creating an inherent weakness at the coupling point. In addition, there was always the possibility of misalignment of either the guide means or the screw, and since the coupling for the screw and for the guide means were located longitudinally together, both the screw and the guide means could be misaligned at the coupling, resulting in damage to the door operator, or even causing the door operator to be inoperative if the misalignment was server enough.